The invention relates to a cylinder head of an internal combustion engine with an electrohydraulic valve controller, which comprises                at least one master unit driven by a camshaft,        at least one valve-side slave unit,        at least one electrically controllable hydraulic valve,        at least one pressure relief space,        and at least one variable volume pressure space, which is arranged in a transmission direction between the associated master unit and the associated slave unit and which can be connected via the associated hydraulic valve to the associated pressure relief space.        
Here, at least the master unit, the slave unit, the pressure space, the hydraulic valve, the pressure relief space, and at least one non-return valve, in combination with a common hydraulic housing, belong to a preassembled hydraulic unit, which is fastened to the cylinder head and which is connected to the hydraulic medium supply of the internal combustion engine via the non-return valve opening in the direction of the hydraulic unit.
Internal combustion engines with an electrohydraulic valve controller, in which the essential components necessary for hydraulic transmission from raised cam sections to the gas-exchange valves are arranged in a preassembled hydraulic unit fastened to the cylinder head, are found in the state of the art. For example, in EP 1 338 764 B1, which is considered to be class forming and which is also to be considered as a reference for the present invention, a cylinder head with a hydraulic unit attached to this head is disclosed. This is formed in a first construction as a hydraulic housing that is independent of the camshaft support, having the master units, slave units, hydraulic pressure storage devices, and also the attachment and connection channels arranged in this housing. In a second construction, the support positions and the lubricant supply for the camshaft are also integrated into the hydraulic housing.
A prerequisite necessary for the trouble-free functioning of the electrohydraulic valve controller is naturally its sufficient supply with an ideally non-compressible hydraulic medium that is practically free from gas bubbles as much as possible. Such a supply can be guaranteed during the operation of the internal combustion engine by the connection of the hydraulic unit to the hydraulic or lubricant supply of the internal combustion engine and, if necessary, through suitable devices for separation of gas bubbles from the hydraulic unit. In the off state of the internal combustion engine, the non-return valve opening in the direction of the hydraulic unit prevents a reverse flow of hydraulic medium into the hydraulic medium supply and thus the generation of gas bubbles within the hydraulic unit. These means proposed in the cited publication, however, do not take into account the situation of the initial assembly of the hydraulic unit in the cylinder head or its reassembly in the case that the internal combustion engine is serviced or repaired. In this situation, it can be provided to mount the hydraulic unit preassembled, but not or not completely filled, in the cylinder head. A subsequent start-up process of the internal combustion engine could then fail because the raised cam sections are not transferred to the gas-exchange valves due to gas bubbles between the master units and the slave units and thus these gas-exchange valves remain closed. Successful start-up or restart of the internal combustion engine would then be possible at best after a considerable and unacceptable delay time, during which the internal combustion engine runs at the starter rotational speed and filling or refilling of the hydraulic unit is dependent on the already time-delayed and moreover inadequate pressure build-up in the hydraulic medium supply.